Actor Sean Astin says tying up his running shoes for Team MR8 in Monday's Boston Marathon was an "overwhelming and gratifying experience" and he comes away with powerful lessons.

The "Rudy" and "Goonies" star was one of 73 members of the team formed in the memory of the 2013 bombing's youngest victim, Martin Richard, 8.

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"I did what I said and tried to honor young Martin Richard (8yrs old) as I passed the site of the tragedy, by reflecting on everything that happened that day and since," he wrote on Facebook.

He said he saw Martin's family, including his sister, Jane, who was also injured in the attacks, cheering him on as he neared the finish line.

"There they were, Jane (9yrs old), standing, jumping up and down, with her prosthetic leg, courtesy of that awful day and Martin's mom, Denise with a huge smile of, can you believe it, gratitude of all things. A smile back and a kiss on the hand later, I turned and lost it," he wrote.

"This family, no fear, not a shred of perceptible anxiety, even if they privately had some. They were enjoying themselves. What a lesson. What an incredible demonstration, not just of resilience and faith and goodness, but of grace and wisdom. It's people like this that are the best hope for advancing our too often beleaguered civilization. This is what progress looks like," he wrote.

Astin, who finished the race in 4:49:53, thanked his supporters for sponsoring his run that raised $22,000 for Team MR8. In all, the group raised about $780,000.